The nomination of James Mattis as Secretary of Defense briefly brought the often overlooked concept of civilian control of the military to public attention. Commentators debated whether Mattis’ qualifications, personality, and presumed influence on the administration justified an exception to the law prohibiting recently retired generals from serving in that post. Reassuringly, in that discussion as well as in the larger conversation about the unusual number of retired and acting general officers now serving in traditionally civilian posts, there has been no discernible challenge to the notion of civilian control of the military. Yet underneath this consensus as to the desirability of civilian control, hide differences in understanding about what it actually entails. In short, we want civilian control but do not precisely know what it is.